I'm using MacOS HIGH SIERRA v.10.13.6, 2,8 GHz processor8 GHz processor, 8 GB 1867 MHz DDR3! Is there any way to convert digitized negatives to positives in this system?

In addition to léonie´s answer - you could save that inverse curve as a custom effect. So you could add that saved effect during import automatically.

Color negatives or Black& White negatives?

The best method would be to use scanning software like vuescan. It knows the gradation curves of many brands of film and will give the best color esults.

For black-and-white negatives you can use the Curves adjustment (this will work in Aperture as well as in Photos).

Try the following:

• Add the Curves adjustment to the Adjustment panel with "Add Adjustment".
• Then modify the RGB curve to shift White to Black and Black to White

This will create a Negative.